Polydactylism
Polydactyly is a relatively common condition in which extra digits on the foot or hand develop during growth of the fetus. This essay presents a discussion of the organs and cells which are affected, along with a discussion of the genetic basis of the condition. Finally, there is a brief discussion of the treatments which are available for the condition.
Specific Organs and Systems Affected
Polydactylism is a condition which results in duplicated digits on the hand or foot (Turra et al., 2007). These range from being small pieces of soft tissue to being fully formed in appearance (NationMaster, 2005). It is noted that in around 80% to 90% of cases involve the peripheral digits, although it is possible that all digits may be affected. Due to the development patterns of polydactylism the classification of the disorder is based on digits affected, as the condition starts peripherally and then spreads to the centre (Borisch et al., 1995). Postaxial polydactyly is that in which it is the fifth digit of the hands or feet which is duplicated. Furthermore, there are two different phenotypes of this form of polydactyly which have been described: type a and type B. In type a, the extra digit is well formed, and in some cases may appear almost whole. In contrast, type B is characterized instead by a rudimentary extra digit (Zhao et al., 2002). A study by Watson and Hennrikus (1997) suggested that in type B polydactyly it may be relatively common to find bilateral polydactyly of the hands. Their study found that 76% of those having duplicated fingers had them on both hands to some extent.
It is possible that polydactylism may occur in isolation or that it may occur as only one element of a more complex condition. For example polydactylism may occur as one element of Bardet-Biedl syndrome. This is an autosomal recessive condition which is also characterized by obesity, mental retardation, short stature and a number of other physical manifestations (Palmer, 2006). This is one of numerous different conditions which may include some form of polydactylism as a characteristic symptom.
Specific Cells Affected
Relatively early work into the cellular developmental process involved in development of polydactylism showed that it is caused by a defect in the cell death process in the embryo. In particular, Scott et al. (1977) found that when the lifespan of ectodermal cells was prolonged this led to an increase in the inductive activity of the underlying mesoderm. It was this increased activity which then created the excess tissue which resulted in the extra digits. This therefore was suggestive of an underlying fault in the cell death process which resulted in prevention of death of these ectodermal cells.
Work by Klein and colleagues (1981) with rat models examined the effect of giving pregnant rats high doses of aspirin. On observation it was found that this created a unique pattern of preaxial mesodermal cell death in hindlimb buds. This pattern involved a delay of the normal cell death which occurred in preaxial apical ectodermal ridge. In addition, there was also a complete absence of cell death in a specific zone of physiological necrosis within the preaxial mesoderm, the same area which is believed to be critical in preaxial digit formation.
More recent work has shown that the identity and number of digits is determined in the embryo by patterning along the antero-posterior axis of the developing limb (Tickle, 2006). This is controlled by a zone of polarizing activity (ZPA), the cells of which produce a signaling molecule sonic hedgehog (SHH) to control the patterning process. It is therefore the mechanism which regulates Shh gene expression which is implicated in polydactylism, specifically preaxial polydactylism. There is a cis-acting regulatory element which has been identified as driving Shh expression, and it is this which has been suggested to be the primary location of mutations in the condition (Hill, 2007). Maas and Fallon (2005) also found that the ectopic expression of Shh in the anterior region of the developing limb in contrast to only the normal posterior expression was associated with polydactyly. This study also discussed the discovery of an enhancer of the Shh gene expression which is found around 1 Mb upstream from the Shh transcription initiation site. This regulatory element is known as ZRS. Despite this being a long-range effector, it is thought that this may also play a role in polydactyly development. Work by Gurnett and colleagues (2007) found that point mutations in ZRS were present in those with triphalangeal thumb, which is further evidence that genetic defects in this part of the cell may be a causative factor in polydactyly.
Genetics
There is some debate over the precise incidence of polydactylism, although it estimated that the condition has an incidence of around 2 children in every 1000, although this is known to vary by population (NationMaster, 2005). It is possible that polydactylism may be a result of hereditary causes in some cases. Preaxial polydactyl in particular has been shown to have a number of different genetic causes (Hill, 2007). One of the most common is that which maps to the human chromosome 7q36, and this is known to occur in one in around 2000 births. In this instance it is a t (5,7)(q11,q36) translocation which has been shown to be crucial in creating the polydactyl phenotype (Lettice et al., 2002). Work by Maas and Fallon (2005) also supported the concept that the genetic basis for preaxial polydactyly is likely to be due to a single base pair change.
A study by Kuru and colleagues (2006) in Turkey investigated a family in which polydactylism of both hands and feet had been identified some years ago. The study found that over time there was an increase in offspring who were homozygous for the condition. These homozygous offspring still displayed clinical polysyndactylism in which digits were underdeveloped, unshaped and fused. The study also found that from both clinical and surgical perspectives the deformations of offspring were different to those of their parents. Although this homozygous polydactylism is considered a separate strain of polysyndactyly it demonstrates that it is possible that the condition may not be a recessive trait.
Studies have also been conducted into the genetic basis of postaxial polysyndactyly. A screening study of 11,161 newborns in America suggests that postaxial polydactyly, particularly type B polydactyly, may be more common than preaxial polydactyly. This study found an incidence of one in 531 births, and of these cases, 86% had a family history of the condition (Watson & Henrikus, 1997). Zhao and colleagues (2002) found that in some cases of postaxial polysyndactyly in the Chinese population, the condition was caused by mutations in the GLI3 gene, and some cases were also associated with a second locus on chromosome 13.
Another study by Boeing et al. (2001) in Brazil also found that family history was a predictive factor in congenital malformation. In addition to this, the study also suggested that ethnicity may play a role in increasing risk. Researchers found that those with African ancestry were at increased risk of developing polydactylism. This echoes earlier work which also suggested that there was an excess of a mild form of polydactylism in black populations (Kalter, 2003).
Aside from hereditary causes, it is also possible that environmental effects could cause the genetic defects in the fetus. Various studies into animal models have identified a number of environmental elements which may create teratogenic effects such as those seen in polydactylism. One example is the study by Saito and colleagues (2006) which found that strong magnetic fields may lead to the development of polydactylism in exposed fetuses among other deformities. Other examples of environmental effects which have received significant attention in relation to congenital birth defects such as polydactyly are maternal habits such as smoking and alcohol consumption. West and colleagues (1981) conducted a study into the impact of dosing maternal rats with ethanol and found that this resulted in the occurrence of polydactyly in offspring.
Therapies or Treatments
The main treatment for polydactylism is surgery, and this is successful in the majority of cases (Turra et al., 2007). The specific type of abnormality which is present must be considered when planning the surgery, and may also play a role in the success of the procedure. For example the procedure is likely to differ dependent on the stage of development of the duplicated digits (Masada et al., 1987). One example of this is discussed by Ataru et al. (2005) who describe the possible complications where the excess toe is adherent to the original toe. The surgical procedure in this type of case must consider which is optimal for removal, the original digit of the excess digit. The main complication which is noted in this type of surgical procedure is that a skin graft may often be required due to a lack of sufficient skin in the area to seal the procedure.
Watson and Hennrikus (1997) describe a procedure whereby duplicated small fingers may be removed relatively simply in the newborn nursery by suture ligation at the base of the pedicle. This would clearly be preferable to performing surgery, but may be more applicable in cases of type B than type a polydactyly. Of a total of 21 cases which were examined, this procedure resulted in a slight complication in only one case, where the digit had to be removed surgically due to failure of removal by suture ligation. The only real side effect of this simple treatment is that there was found to be a small bump remaining at the site in 43% of cases.
Conclusion
Although there has been some work into the genetic basis of polydactyly, advances in examination of the human genome may create a better understanding of the condition in the future. A large amount of the work done so far has been focused on animal models, and there is still room for further work to discover the genetic basis of the different types of polydactyly in humans.
References
Ataru, S., Park, S. & Ryo, Y. (2005). Surgical treatment for lateral ray polydactyly of the foot: Toe selection and interdigital space reconstruction using a planter flap. Japanese Journal of Plastic & Reconstructive Surgery, 48(2): 155-159.
Boeing, M., Cassia F. Paiva, L., Lima Garcias, G., Graca Martino Roth, M. & Santos, I.S. (2001). Epidemiologia das polidactilias: Um estudo de casos e controles na populacao de Pelotas-RS. Journal de Pediatria, 77(2); d.o.i.: 10.1590/S0021-7557200100017.
Borisch, N., Stunitz, B. & Blauth, W. (1995). Case histories surgical treatment of polydactyl of the little toe involving proximal and middle phalanx. Orthopedics and Traumatology, 4(4): 246-253.
Gurnett, C.A., Bowcock, a.M., Dietz, F.R., Morcuende, J.A., Murray, J.C. & Dobbs, M.B. (2007). Two novel point mutations in the long-range SHH enhancer in three families with triphalangeal thumb and preaxial polydactyly. American Journal of Medical Genetics, 143(1): 27-32.
Hill, R.E. (2007). How to make a zone of polarizing activity: Insights into limb development via the abnormality preaxial polydactyl. Developmental Growth Differ., 49: 439-448.
Kalter, H. (2003). Teratology in the 20th century environmental causes of congenital malformations in humans and how they were established. Neurotoxicology and Teratology, 25(2): 131-282.
Klein, K.L., Scott, W.J. & Wilson, J.G. (1981). Aspirin-induced teratogenesis: A unique pattern of cell death and subsequent polydactyly in the rat. Journal of Experimental Zoology, 216(1): 107-112.
Kuru, I., Maralcan, G., Yucel, a., Aktepe, F., Turkmen, S. & Solak, M. (2006). Synpolydactyly of the foot in homozygotes. Journal of the American Podiatric Medical Association, 96(4): 297-304.
Lettice, L.A., Horikoshi, T. & Heaney, S.J. (2002). Disruption of a long-range cis-acting regulator for Shh causes preaxial polydactyl. Proceedings of the National Academy of Sciences, 99: 7548-7553.
Maas, S.A. & Fallon, J.F. (2005). Single base pair change in the long-range Sonic hedgehog limb-specific enhancer is a genetic basis for preaxial polydactyly. Developmental Dynamics, 232(2): 345-348.
Masada, K., Tsuyuguchi, Y., Kawabati, H. & Ono, K. (1987). Treatment of preaxial polydactyl of the foot. Plastic & Reconstructive Surgery, 79(2): 251-258.
NationMaster (2005). Polydactylism. NationMaster Encyclopedia. Retrieved on November 14, 2008, at http://www.nationmaster.com/encyclopedia/Polydactylism.
Palmer, J.S. (2006). Genitourinary manifestations in boys and girls associated with genetic diseases. The Journal of Men’s Health & Gender, 3(1): 71-79.
Saito, K., Suzuki, H. & Suzuki, K. (2006). Teratogenic effects of static magnetic field on mouse fetuses. Reproductive Toxicology, 22(1): 118-124.
Scott, W.J., Ritter, E.J. & Wilson, J.G. (1977). Delayed appearance of ectodermal cell death as a mechanism of polydactyly induction. Journal of Embryology Experimental Morphology, 42: 93-104.
Turra, S., Gigante, C. & Bisinella, G. (2007). Polydactyl of the foot. Journal of Pediatric Orthopaedics B, 16(3): 216-220.
Watson, B.T. & Hennrikus, W.L. (1997). Postaxial type-B polydactyly. Prevalence and treatment. The Journal of Bone and Joint Surgery, 79: 65-68.
West, J.R., Black, a.C., Reimann, P.C. & Alkana, R.L. (1981). Polydactyly and polysyndactyly induced by prenatal exposure to ethanol. Teratology, 24(1): 13-18.
Zhao, H., Tian, Y., Breedveld, G., Huang, S., Zou, S., Y, Jue, Chai, J., Li, M., Oostra, B.A., Lo, W.H.Y & Heutink, P. (2002). Postaxial polydactyl type a/B (PAP-a/B) is linked to chromosome 19p13.1-13.2 in a Chinese kindred. European Journal of Human Genetics, 10(3): 162-166.
Polydactylism
Are you busy and do not have time to handle your assignment? Are you scared that your paper will not make the grade? Do you have responsibilities that may hinder you from turning in your assignment on time? Are you tired and can barely handle your assignment? Are your grades inconsistent?
Whichever your reason is, it is valid! You can get professional academic help from our service at affordable rates. We have a team of professional academic writers who can handle all your assignments.
Students barely have time to read. We got you! Have your literature essay or book review written without having the hassle of reading the book. You can get your literature paper custom-written for you by our literature specialists.
Do you struggle with finance? No need to torture yourself if finance is not your cup of tea. You can order your finance paper from our academic writing service and get 100% original work from competent finance experts.
Computer science is a tough subject. Fortunately, our computer science experts are up to the match. No need to stress and have sleepless nights. Our academic writers will tackle all your computer science assignments and deliver them on time. Let us handle all your python, java, ruby, JavaScript, php , C+ assignments!
While psychology may be an interesting subject, you may lack sufficient time to handle your assignments. Don’t despair; by using our academic writing service, you can be assured of perfect grades. Moreover, your grades will be consistent.
Engineering is quite a demanding subject. Students face a lot of pressure and barely have enough time to do what they love to do. Our academic writing service got you covered! Our engineering specialists follow the paper instructions and ensure timely delivery of the paper.
In the nursing course, you may have difficulties with literature reviews, annotated bibliographies, critical essays, and other assignments. Our nursing assignment writers will offer you professional nursing paper help at low prices.
Truth be told, sociology papers can be quite exhausting. Our academic writing service relieves you of fatigue, pressure, and stress. You can relax and have peace of mind as our academic writers handle your sociology assignment.
We take pride in having some of the best business writers in the industry. Our business writers have a lot of experience in the field. They are reliable, and you can be assured of a high-grade paper. They are able to handle business papers of any subject, length, deadline, and difficulty!
We boast of having some of the most experienced statistics experts in the industry. Our statistics experts have diverse skills, expertise, and knowledge to handle any kind of assignment. They have access to all kinds of software to get your assignment done.
Writing a law essay may prove to be an insurmountable obstacle, especially when you need to know the peculiarities of the legislative framework. Take advantage of our top-notch law specialists and get superb grades and 100% satisfaction.
We have highlighted some of the most popular subjects we handle above. Those are just a tip of the iceberg. We deal in all academic disciplines since our writers are as diverse. They have been drawn from across all disciplines, and orders are assigned to those writers believed to be the best in the field. In a nutshell, there is no task we cannot handle; all you need to do is place your order with us. As long as your instructions are clear, just trust we shall deliver irrespective of the discipline.
Our essay writers are graduates with bachelor's, masters, Ph.D., and doctorate degrees in various subjects. The minimum requirement to be an essay writer with our essay writing service is to have a college degree. All our academic writers have a minimum of two years of academic writing. We have a stringent recruitment process to ensure that we get only the most competent essay writers in the industry. We also ensure that the writers are handsomely compensated for their value. The majority of our writers are native English speakers. As such, the fluency of language and grammar is impeccable.
There is a very low likelihood that you won’t like the paper.
Not at all. All papers are written from scratch. There is no way your tutor or instructor will realize that you did not write the paper yourself. In fact, we recommend using our assignment help services for consistent results.
We check all papers for plagiarism before we submit them. We use powerful plagiarism checking software such as SafeAssign, LopesWrite, and Turnitin. We also upload the plagiarism report so that you can review it. We understand that plagiarism is academic suicide. We would not take the risk of submitting plagiarized work and jeopardize your academic journey. Furthermore, we do not sell or use prewritten papers, and each paper is written from scratch.
You determine when you get the paper by setting the deadline when placing the order. All papers are delivered within the deadline. We are well aware that we operate in a time-sensitive industry. As such, we have laid out strategies to ensure that the client receives the paper on time and they never miss the deadline. We understand that papers that are submitted late have some points deducted. We do not want you to miss any points due to late submission. We work on beating deadlines by huge margins in order to ensure that you have ample time to review the paper before you submit it.
We have a privacy and confidentiality policy that guides our work. We NEVER share any customer information with third parties. Noone will ever know that you used our assignment help services. It’s only between you and us. We are bound by our policies to protect the customer’s identity and information. All your information, such as your names, phone number, email, order information, and so on, are protected. We have robust security systems that ensure that your data is protected. Hacking our systems is close to impossible, and it has never happened.
You fill all the paper instructions in the order form. Make sure you include all the helpful materials so that our academic writers can deliver the perfect paper. It will also help to eliminate unnecessary revisions.
Proceed to pay for the paper so that it can be assigned to one of our expert academic writers. The paper subject is matched with the writer’s area of specialization.
You communicate with the writer and know about the progress of the paper. The client can ask the writer for drafts of the paper. The client can upload extra material and include additional instructions from the lecturer. Receive a paper.
The paper is sent to your email and uploaded to your personal account. You also get a plagiarism report attached to your paper.
GET A PERFECT SCORE!!! 
Delivering a high-quality product at a reasonable price is not enough anymore.
That’s why we have developed 5 beneficial guarantees that will make your experience with our service enjoyable, easy, and safe.
You have to be 100% sure of the quality of your product to give a money-back guarantee. This describes us perfectly. Make sure that this guarantee is totally transparent.
Read moreEach paper is composed from scratch, according to your instructions. It is then checked by our plagiarism-detection software. There is no gap where plagiarism could squeeze in.
Read moreThanks to our free revisions, there is no way for you to be unsatisfied. We will work on your paper until you are completely happy with the result.
Read moreYour email is safe, as we store it according to international data protection rules. Your bank details are secure, as we use only reliable payment systems.
Read moreBy sending us your money, you buy the service we provide. Check out our terms and conditions if you prefer business talks to be laid out in official language.
Read more